Huge Artesian Well

Sun (Auckland), Volume I, Issue 163, 30 September 1927, Page 8

Huge Artesian Well

Lake Pupuke Investigation 44 Cannot Be Pumped Dry” North Shore Water Supply NOT a sump for rain water but a huge natural artesian well which cannot be pumped dry. This opinion of Lake Pupuke, Takapuna, has been arrived at by Mr. A. Slinger, Takapuna Borough Engineer, after thorough investigations.

' r T'HE lake could never be pumped dry, though its level might possibly be lowered another 10 feet,” says Mr. Slinger. Soundings taken over this gigantic self-filling reservoir indicated that the maximum depth was 165 ft below zero on the gauge and that the convex bottom was soft ooze Into which the sounding weight sank quickly; w-hereas it might have been expected that after unnumbered

* * w **shk**;** * * * * centuries of precipitation the bottom would have been almost solid. The inference was that water was making its way upward through the lake bottom. SUBTERRANEAN SUPPLY On the west side of the lake a line of moisture seeking willows indicated a hidden stream; investigation showed a filled-up valley leading toward the headwaters of the Wairau Stream. A well sunk on the line of this valley, at a point three-quarters of a mile from the lake, at a depth of 52ft, gave a sustained supply of 45,000 gallops daily, enough to supply Takapuna. A little closer to the lake, on a slope above the Wairau Stream, a bore put down 960 ft gave an artesian supply of first-class water and this is still used by householders in the neighbourhood. The remarkable fact

is that the artesian bore mouth is 32ft above lake level. Another interesting discovery was that the Wairau valley lias been filled up to a depth of 14ft by detritus. More evidence of subterranean supply to the lake is the “lag” in the rise of the lake level after heavy rains: a matter of months, w-hereas the run-off from the catchment area reaches the lake in a matter of hours. The engineers have, estimated that the rain water fed to the lake amounts from 150 to 200 million gallons per annum, but the pumps have been lifting 352 million gallons per annum from the lake! The evidence all points to the fact that below the Waitemata beds of stratified sandstone that overlay the isthmus there is stored water. The beds are estimated to be about I,oooft thick and no bore has yet penetrated that depth; the volcanic rent of the Pupuke crater unquestionably did and it serves as a gigantic artesian bore carrying water to the natural reservoir, which also has the benefit of some rainfall. 100 YEARS’ SUPPLY “The lake w-ould last the marine boroughs for 100 years if kept free from pollution,” was the summing up of Mr. Slinger. This would mean buying £200,000 worth of land around the lake, but the land would be an asset. The recent water commission recommended that the lake be kept as a permanent supply, helped out by the Rangitopuni Stream which runs in a valley below Albany; this would allow of giving water to the bays beyond Milford; would be 2d a 1,000 gallons cheaper than the proposed Waitakere scheme, and would postpone the time when Auckland City would have to go further afield than the Waitakeres for its water. The commission, while not examining the possibility of artesian supply to the lake, urged the combining of the three pumping plants now operating. The North Shore Water Board has leaned to the Waitakere scheme and the abandonment of the lake. Just a few weeks ago it was made public that there had been in Devonport a "wastage, at the electric-power station, of 40,000,000 gallons per annum; an amount that: would have supplied Northcote Borough; so that eliminating waste, the lake could meet a considerably increased demand without becoming depleted any further than it is now, and without approaching the minimum level beyond which the runin to the lake from nearby and distant rainfall would establish a balance with the draw-off.